Transport systems responsible for the absorption by the small intestine and reabsorption by the renal proximal tubule of nutritionally important substrates will be investigated with isolated plasma membrane vesicles and liposomes. Inside-out and right-side-out intestinal and renal brush border and basolateral membrane vesicles will be employed in uptake studies with monosaccharides, amino acids, calcium and phosphate. Na ion-independent sugar and amino acid uptake and Na ion-coupled active amino acid uptake will be characterized with plasma membrane vesicles prepared from fed and fasted animals. Calcium uptake will be studied with plasma membrane vesicles obtained from control, vitamin D-depleted, vitamin D-repleted and cortisone and parathyroid hormone treated animals. The uptake of phosphate will also be measured with these plasma membrane vesicles except those from cortisone treated animals. Liposomes containing extracted proteins from control and experimental intestinal and renal plasma membranes will be employed in uptake studies similar to those conducted with plasma membrane vesicles. In addition, dipeptide and sodium uptake will be observed with these liposomes. The reconstitution of specific transport systems will be related to the homogeneity, enzyme activities and the molecular weights of the constituents within the membrane protein fractions incorporated into the liposome bilayer.